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Abstract:

The invention provides a process for the preparation of hydrocarbons
comprising the steps of: (a) contacting a mixture of carbon monoxide and
hydrogen at an elevated temperature and pressure with a mixture of a
methanol synthesis catalyst and a methanol conversion catalyst thereby
forming C5.sup.+ hydrocarbons; (b) separating at least part of the
C5.sup.+ hydrocarbons as obtained in step (a) into a light stream
and a heavy durene-rich stream; (c) subjecting at least part of the heavy
durene-rich stream to a hydrodealkylation treatment in the presence of
hydrogen to obtain a stream of hydrocarbons having a reduced durene
content; and (d) mixing at least part of the light stream as obtained in
step (b) with at least part of the stream of hydrocarbons having a
reduced durene content as obtained in step (c).

Claims:

1. A process for the preparation of hydrocarbons comprising the steps of:
(a) contacting a mixture of carbon monoxide and hydrogen at an elevated
temperature and pressure with a mixture of a methanol synthesis catalyst
and a methanol conversion catalyst thereby forming C.sub.5.sup.+
hydrocarbons; (b) separating at least part of the C.sub.5.sup.+
hydrocarbons as obtained in step (a) into a light stream and a heavy
durene-rich stream; (c) subjecting at least part of the heavy durene-rich
stream to a hydrodealkylation treatment in the presence of hydrogen to
obtain a stream of hydrocarbons having a reduced durene content; and (d)
mixing at least part of the light stream as obtained in step (b) with at
least part of the stream of hydrocarbons having a reduced durene content
as obtained in step (c).

2. A process according to claim 1, wherein the methanol synthesis
catalyst comprises a zinc-containing composition which, in addition to
zinc, comprises one or more metals chosen from chromium, copper and
aluminium.

3. A process according to claim 2, wherein the methanol synthesis
catalyst is a ZnO--Cr2O3 catalyst.

4. A process according to claim 1, wherein the weight ratio of the
methanol synthesis catalyst to the methanol conversion catalyst is in the
range of from 0.1-12.5.

5. A process according to claim 1, wherein the methanol conversion
catalyst comprises a crystalline (metallo)silicate comprising in addition
to SiO2 one or more oxides of a trivalent metal chosen from
aluminium, iron, gallium, rhodium, chromium and scandium, and having a
SiO2/Al2O3 molar ratio of at least 10.

6. A process according to claim 5, wherein the methanol conversion
catalyst is a crystalline iron alumina silicate or a zeolite selected
from the group consisting of ZSM-5, ZSM-11, ZSM-12, ZSM-35 and ZSM-38.

7. A process according to claim 1, wherein step (a) is carried out at a
temperature of 200-500.degree. C., a pressure of 1-150 bar and a space
velocity of 50-10000 N1.1.sup.-1.h.sup.-1.

8. A process according to claim 1, wherein the mixture of carbon monoxide
and hydrogen in step (a) has a H2/CO molar ratio in the range of
from 0.3-2.

9. A process according to claim 1, wherein the separation in step (b) is
carried out at a temperature in the range of from 150-190.degree. C.

10. A process according to claim 1, wherein the heavy durene-rich stream
as obtained in step (b) contains C.sub.8.sup.+ aromatics in an amount in
the range of from 50 to 99 wt %, based on total weight of the heavy
durene-rich stream.

11. A process according to claim 1, wherein the hydrodealkylation
treatment is a catalytic hydrodealkylation treatment.

12. A process according to claim 1, wherein the entire light stream as
obtained in step (b) is mixed with the entire stream of hydrocarbons
having a reduced durene content as obtained in step (c).

Description:

[0001] This application claims the benefit of European Application No.
10187160.6 filed Oct. 11, 2010, which is incorporated herein by
reference.

FIELD OF THE INVENTION

[0002] The present invention relates to a process for the preparation of
hydrocarbons, in particular gasolines and aromatic hydrocarbons.

BACKGROUND OF THE INVENTION

[0003] Many documents are known describing methods and processes for the
conversion of synthesis gas into hydrocarbons. The preparation of
hydrocarbons from a H2/CO mixture by contacting this mixture at elevated
temperature and pressure with a catalyst is known in the literature as
the Fischer-Tropsch hydrocarbon synthesis. Catalysts often used for the
purpose comprise one or more metals from the iron group, together with
one or more promoters, and a carrier material. These catalysts can
suitably be prepared by known techniques, such as precipitation,
impregnation, kneading and melting. The products which can be prepared by
using these catalysts generally have a very wide molecular weight
distribution range. In addition to branched and unbranched paraffins,
they often contain considerable amounts of olefins, oxygen-containing
organic compounds and heavy aromatic hydrocarbons. Therefore, the direct
conversion of H2/CO mixtures using the Fischer-Tropsch synthesis is not a
very attractive route for the production of gasolines that meet
environmental specifications.

SUMMARY OF THE INVENTION

[0004] It has now been found that attractive gasoline components and
aromatic hydrocarbons can be produced when use is made of a particular
multi-step conversion process.

[0005] Accordingly, the present invention provides a process for the
preparation of hydrocarbons comprising the steps of: [0006] (a)
contacting a mixture of carbon monoxide and hydrogen at an elevated
temperature and pressure with a mixture of a methanol synthesis catalyst
and a methanol conversion catalyst thereby forming C5.sup.+
hydrocarbons; [0007] (b) separating at least part of the C5.sup.+
hydrocarbons as obtained in step (a) into a light stream and a heavy
durene-rich stream; [0008] (c) subjecting at least part of the heavy
durene-rich stream to a hydrodealkylation treatment in the presence of
hydrogen to obtain a stream of hydrocarbons having a reduced durene
content; and [0009] (d) mixing the at least part of the light stream as
obtained in step (b) with at least part of the stream of hydrocarbons
having a reduced durene content as obtained in step (c). An advantage of
the present invention is that attractive gasoline components can be
prepared, whereas at the same time valuable aromatic hydrocarbons can be
produced for use as base chemicals for the production of a wide range of
organic compounds. This combined production of gasoline components and
aromatics is particularly attractive in view of the increasing demand for
aromatics in the production of a wide variety of petrochemical compounds.
This especially applies to benzene.

DETAILED DESCRIPTION OF THE INVENTION

[0010] The invention provides a process for the preparation of
hydrocarbons that can be used as gasoline components or as base chemicals
in the chemical industry.

[0011] In step (a) a mixture of carbon monoxide and hydrogen is converted
into a hydrocarbon mixture whose C5.sup.+ fraction has a high
content of branched C5 and C6 paraffins.

[0012] Suitably, step (a) is carried out at a temperature of
200-500° C., preferably in the range of from 300-450° C., a
pressure in the range of from 1-150 bar, preferably in the range of from
5-100 bar, and a space velocity in the range of from 50-10000
N1.1-1.h-1, preferably in the range of from 300-3000
N1.1-1.h-1.

[0014] Preferably, the mixture of carbon monoxide and hydrogen in step (a)
has a H2/CO molar ratio in the range of from 0.3-2, more preferably
in the range of from 0.4-1.

[0015] In step (a) use is made of a mixture of a methanol synthesis
catalyst and a methanol conversion catalyst.

[0016] The methanol synthesis catalyst to be used in accordance with the
present invention suitably comprises a zinc-containing composition which,
in addition to zinc, comprises one or more metals chosen from chromium,
copper and aluminium. The zinc-containing composition can suitably be
prepared starting from one or more precipitates obtained by adding a
basic reacting substance to one or more aqueous solutions containing
salts of the metals involved.

[0017] Preferably, the methanol synthesis catalyst is a
ZnO--Cr2O3 catalyst. Preferably, the atomic percentage of zinc
calculated on the sum of zinc and chromium is 60-80%.

[0018] The methanol conversion catalyst to be used in accordance with the
present invention suitably comprises a crystalline (metallo)silicate
comprising in addition to SiO2 one or more oxides of a trivalent
metal chosen from aluminium, iron, gallium, rhodium, chromium and
scandium, and having a SiO2/Al2O3 molar ratio of at least
10.

[0019] Preferably, the methanol conversion catalyst is a crystalline iron
alumina silicate or a zeolite selected from the group consisting of
ZSM-5, ZSM-11, ZSM-12, ZSM-35 and ZSM-38. ZSM-5 is particularly preferred
as zeolite.

[0020] The crystalline (metallo)silicate has suitably after one hour's
calcination in air at 500° C., the following properties: (a) an
X-ray powder diffraction pattern in which the strongest lines are the
four lines mentioned in Table A,

[0021] In case the methanol conversion catalyst is a crystalline iron
alumina silicate suitably the
SiO2/((Fe2O3+Al2O3) molar ratio is higher than
10, the SiO2/Fe2O3 molar ratio is suitably lower than 250
and the SiO2/Al2O3 molar ratio is suitably at least 50.
The crystalline iron alumina silicate has preferably a
SiO2/Fe2O3 molar ratio higher than 25, but lower than 250
and a SiO2/Al2O3 molar ratio of at least 50, but lower
than 1200. More preferably, the crystalline iron alumina silicate has a
SiO2/Fe2O3 molar ratio of 50-175 and a
SiO2/Al2O3 molar ratio of at least 50, but lower than 800.
In case the methanol conversion catalyst is a crystalline iron silicate,
the SiO2/Fe2O3 molar ratio is suitably higher than 25, but
lower than 250. Preferably, the crystalline iron silicate has a
SiO2/Fe2O3 molar ratio in the range of from 50-175.

[0022] Suitably, the crystalline (metallo)silicate has an alkali metal
content of less than 0.05% w.

[0023] In step (a) the weight ratio of the methanol synthesis catalyst to
the methanol conversion catalyst is suitably in the range of from
0.1-12.5, and preferably in the range of from 0.5-10, and more preferably
in the range of from 2.5-8,

[0024] The crystalline iron alumina silicates can be prepared starting
from an aqueous mixture comprising the following compounds: one or more
silicon compounds, one or more compounds which contain a monovalent
organic cation (R) of from which such a cation is formed during the
preparation of the silicate, one or more compounds in which iron and
aluminium are present in trivalent form and one or more compounds of an
alkali metal (M). The preparation is carried out by keeping the mixture
at an elevated temperature until the silicate has formed, and
subsequently separating the silicate crystals from the mother liquor and
washing, drying and calcining the crystals. In the aqueous mixture from
which the silicates are prepared the various compounds should be present
in the following ratios, expressed in moles of the oxides:

M2O:SiO2<0.35,

R2O:SiO2=0.01-0.5,

SiO2:(Fe2O3+Al2O3)>10, and

H2O:SiO2=5-100.

[0025] If in the preparation of the crystalline silicates the starting
material is an aqueous mixture in which one or more alkali metal
compounds are present, the crystalline silicates obtained will contain
alkali metal. Depending on the concentration of alkali metal compounds in
the aqueous mixture the crystalline silicates obtained may contain more
than 1% w alkali metal. Since the presence of alkali metal in the
crystalline silicates has an unfavourable influence on their catalytic
properties, it is common practice in the case of crystalline silicates
with a relatively high alkali metal content to reduce this content before
using these silicates as catalysts. A reduction of the alkali metal
content to less than 0.05% w is usually sufficient to this end. The
reduction of the alkali metal content of crystalline silicates can very
suitably be effected by treating the silicates once or several times with
a solution of an ammonium compound. During this treatment alkali metal
ions are exchanged for NH4.sup.+ ions and the silicate is converted to
the NH4.sup.+ form. The NH4.sup.+ form of the silicate is converted to
the H.sup.+ form by calcination.

[0026] In the preparation of the catalyst mixtures used in the present
process use is made of one or more precipitates in which zinc occurs
together with chromium and/or aluminium and which precipitates have been
obtained by adding a basic reacting substance to one or more aqueous
solution of salts of the metals involved. Preference is given to the use
of precipitates in which, in addition to zinc, chromium occurs, in
particular precipitates in which the atomic percentage of zinc,
calculated on the sum of zinc and chromium, is at least 60% and more
specifically 60-80%. The metal-containing precipitates may be prepared by
precipitation of each of the metals individually or by co-precipitation
of the desired metal combination. Preference is given to the use of a
co-precipitate obtained by adding a basic reacting substance to an
aqueous solution containing all the metals involved. This
co-precipitation is preferably carried out in a mixing unit with a
continuous supply of an aqueous solution containing the metal salts
involved and an aqueous solution of the basic reacting substance in a
stoichiometric quantity calculated on the metals, and with a continuous
discharge of the co-precipitate formed.

[0027] The preparation of the catalyst mixtures used in the present
process can be carried out in various ways. The precipitate may be
calcined and then mechanically mixed with the crystalline silicate. The
catalyst mixture may also very suitably be prepared by spray-drying. To
this end the crystalline silicate is dispersed in water together with the
precipitate mentioned hereinbefore, the dispersion thus obtained is
spray-dried, and the spray-dried material is calcined. Spray-drying is a
method used on a commercial scale for many years past for the preparation
of small spherical particles from a solid material or a mixture of
solids. The process is carried out by atomizing a dispersion in water of
the material to be spray-dried through a nozzle or from a rotating disc
into a hot gas. The process is particularly suitable for achieving
intimate contact between different materials. In view of the form, size
and strength of the catalyst particles prepared by spray-drying they are
very suitable for use in a fluidized state.

[0028] In step (b) the separation will suitably be carried out at a
temperature in the range of from 150-190° C. Preferably, the
separation in step (b) is carried out at a temperature in the range of
from 155-180° C., more preferably at a temperature in the range of
from 155-170° C.

[0029] In step (b) at least part of the C5.sup.+ hydrocarbons as
obtained in step (a) is separated into a light stream and a heavy
durene-rich stream. The heavy durene-rich stream as obtained in step (b)
suitably contains C8.sup.+ aromatics in an amount in the range of
from 50-99 wt % preferably 85-95 wt % based on total weight of the heavy
durene-rich stream. In the context of the present invention a heavy
durene-rich stream is defined as a stream comprising more than 2 wt % of
durene, based on total weight of the stream. It will be understood that
durene is 1,2,4,5-tetramethylbenzene which is an unwanted by-product in
gasoline synthesis because it solidifies at room temperature. The light
stream as obtained in step (b) will typically not contain C10.sup.+
aromatics, whereas the heavy durene-rich stream will typically contain
C10.sup.+ aromatics in an amount in the range of from 5-60 wt %,
preferably 25-45 wt %, based on total weight of the heavy durene-rich
stream. In the context of the present invention a light stream is defined
as a stream comprising less than 2 wt % of durene, based on total weight
of the stream.

[0030] In step (c) of the process according to the present invention at
least part of the heavy durene-rich stream is subjected to a
hydrodealkylation treatment to obtain a stream of hydrocarbons having a
reduced durene content. The hydrodealkylation is carried out in the
presence of hydrogen and at conditions so as to dealkylate
alkyl-substituted aromatic hydrocarbons. In this process toluene, mixed
xylenes and heavier aromatics are dealkylated to produce benzene, or
toluene is transalkylated to produce benzene and mixed xylenes.

[0031] The hydrodealkylation treatment in step (c) can be a thermal
hydrodealkylation or a catalytic hydrodealkylation. Preferably, use is
made of a catalytic hydrodealkylation treatment.

[0032] In case use is made in step (c) of a thermal hydrodealkylation
treatment, at least part of the heavy durene-rich stream as obtained in
step (b) is passed to a thermal hydrodealkylation reactor. Suitably, such
a reactor comprises a vertical cylindrical vessel with inlet means in the
upper part. It will be understood that in a thermal hydrodealkylation
process no use is made of a catalyst. However, some materials used within
a thermal hydrodealkylation reactor may display some catalytic activity
at the temperatures applied in operation. Suitably, the upper part
(50-66%) of the reactor is empty and the remaining lower part of the
reactor comprises means for providing plug flow, such as for instance
inert vertical baffles or ceramic balls. The thermal hydrodealkylation
treatment can suitably be carried out at a temperature in the range of
from 580-850° C. and a pressure in the range of from 20-60 bar.
The residence time of the heavy durene-rich stream in the reactor will
suitably be in the range of from 4-60 seconds.

[0033] In case use is made in step (c) of a catalytic hydrodealkylation
treatment, at least part of the heavy durene-rich stream as obtained in
step (b) is passed to a hydrodealkylation reactor which includes a
catalyst. The catalytic hydrodealkylation treatment can suitably be
carried out at a temperature in the range of from 480-850° C. and
a pressure in the range of from 20-70 bar. Catalysts to be used in
hydrodealkylation processes are as such well-known. A suitable catalyst
comprises for instance an oxide of a metal of Group VI-B and/or Group
VIII of the Periodic Table on a refractory inorganic oxide. Suitable
Group VI-B metals include chromium, molybdenum, and tungsten. Suitable
Group VIII metals include platinum, nickel, iron, cobalt, rhenium and
manganese. Suitable refractory inorganic oxides include for instance
alumina, alumina-silica and zirconia. A preferred catalyst comprises
chromium composite on a high surface alumina, such as gamma alumina, with
the chromia being present in an amount in the range of from 10-20 wt. %
of chromium oxide, based on the weight of alumina. The liquid hourly
space velocity of the heavy durene-rich stream can suitably be in the
range of from 0.5-5.0 h-1. Suitably, in the reactor a
hydrogen/hydrocarbon molar ratio of from 5-15 is applied.

[0034] In step (d) at least part of the light stream as obtained in step
(b) is mixed with at least part of the stream of hydrocarbons having a
reduced durene content as obtained in step (c). Preferably, the entire
light fraction as obtained in step (b) is mixed with the entire stream of
hydrocarbons having a reduced durene content as obtained in step (c).

[0035] Preferably, at least part of the mixture obtained in step (d) is
passed to an aromatics extraction unit, for instance a Sulfolane
extraction unit. In such an aromatics extraction unit zone benzene and
other aromatics such as toluene and xylenes are separated from
non-aromatics, obtaining an aromatics stream and a non-aromatics stream.
Such aromatics extraction units are as such well-known.

[0036] Subsequently, at least part of the aromatics stream so obtained can
suitably be passed to a fractionation unit, for example a BTX
fractionation unit, wherein the various aromatics are separated from each
other. In this way, a benzene stream, a toluene stream and a stream of
xylenes can for instance be obtained. Such fractionation units are as
such well-known.

Example According to the Invention

Example 1

[0037] The following example has been modelled using PRO/II software as
obtained from Invensys Process Systems, Plano, Houston (USA).

[0039] This example is carried out in the same manner as the Example 1
according to the invention, except that the heavy durene-rich stream was
not subjected to the catalytic hydrodealkylation treatment. In table 1
components of the product so obtained are shown.

[0040] From the results as shown in Table 1, it will be clear that the
present invention provides a highly attractive process for the combined
production of gasoline blend components and aromatics, in particularly
benzene. In accordance with the present invention not only an improved
gasoline is obtained which contains less aromatics, but also much more
benzene per amount of gasoline produced at the same time.